Snowmobile electrical systems typically derive power from a permanent magnet alternator driven by the crankshaft of the engine. These alternators are typically regulated to approximately 14 volts TRMS by an AC shunt regulator such as is shown in applicant's co-pending application, U.S. Ser. No. 08/499,365 filed Jul. 7, 1995 for Power Generation and Regulation Apparatus. The resulting voltage has a constant true RMS value. However, the waveform is non sinusoidal and may have portions of the waveform with very rapid rates of change in voltage with time. The voltage varies in frequency with varying engine speed and the wave shape and form factor vary with the application or removal of various loads. The size of these alternators is restricted by the weight, cost and space available on the vehicle and therefore in many cases they are not capable of running all loads simultaneously at specified voltage particularly at low engine speeds. In addition to lighting and battery charging loads, a known load on vehicles of this type is from electrically heated handlebars. These traditionally have been either turned off, set to low power, or set to high power through an operator controlled switch. AC temperature or voltage control methods typically used with 60 cycle power have proven to be difficult or at best impractical to apply to these circuits because of the previously mentioned variations in frequency and waveform.
Halfwave control techniques, as will be understood by one skilled in the art, are wasteful of electrical energy available from an alternator of this type which has essentially a constant current output. Fullwave control with devices such as a triac is difficult or impossible with the frequency and rate of change of voltage with time sometimes present in these systems. Even though the handlebar heaters will not respond adversely to waveforms which are turned on and off at a relatively low rate, control technology producing this type of switching will cause a noticeable and objectionable flicker in the headlights of the vehicle. Brake lights on vehicles of this type draw a significant amount of power. Therefore, if the handlebar heaters, brake lights and other loads are on simultaneously, significant and potentially dangerous dimming of the headlights can occur at a critical time.
The amount of heat required increases as the temperature of the vehicle operated decreases and also increases with the speed of the vehicle through the air. These vehicles operate over a very wide temperature range. Therefore, it is possible for the amount of heat that is required at low temperature and high speed to cause excessive temperature or destruction of the heating elements or handlebar grips at low speed and moderately warm temperatures.